1. Field of the Invention
The present invention relates to a die casting method and an apparatus therefor.
2. Prior Art
Die casting machines are classified by vertical clamping and lateral clamping type in terms of the die clamping direction, and by vertical casting and lateral casting type in terms of the pouring direction of hot molten metal into a die.
A conventional vertical clamping, vertical casting type of die casting machine is shown in FIG. 27, in longitudinal section form, and is similar to that described, for example, in U.S. Pat. Nos. 4,269,259 and 4,287,935. This conventional die casting machine will be briefly described with reference to this figure. A cylinder platen 1 and a base platen 2 are joined to each other in a vertical direction by means of four tiebars 3. These tiebars 3 support a moving platen 6 vertically movable under the actuation of a main ram 4 and a pull-back cylinder 5. To both the platens 2 and 6, a stationary metal mold 7 and a movable metal mold 8 are respectively mounted to oppose each other. An injection cylinder generally denoted by reference numeral 9 is tiltably supported by means of a pin 12 on a platen 11 provided at the lower end of tiebars 10 suspending from the base platen 2. The injection cylinder has a cylinder 13, a piston rod 13 vertically movable within the cylinder 13 under the application of oil pressure, a plunger 16 joined to the piston rod 14 by means of a coupling 15, a block 18 supported, vertically movably, at the upper end of the cylinder 13, rams 19 studded on the upper surface of the cylinder 13 to vertically move the block 18 under the application of oil pressure, and an injection sleeve 20 mounted to the upper end of the block 18 to allow a head of the plunger 16 to be fitted in the injection sleeve 20. The entirety of the injection cylinder 9 can be tilted from a position indicated by a solid line to a position indicated by a phantom line by operating a tilting cylinder 21 and a swingable link 21a. Additionally provided for a conventional die casting machine, but not shown, are a device for feeding hot molten metal, a device for taking out products and a spraying device.
A casting operation with the die casting machine thus configured will now be described. The moving platen 6 to which the movable metal mold 8 is secured is first lowered by the actuation of the main ram 4 to press the movable metal mold 8 against the stationary metal mold 7, thus completing die clamping. Subsequently the injection cylinder 9 is tilted by the actuation of the tilting cylinder 21 to the position indicated by a phantom line and hot molten metal is poured into the injection sleeve 20 by using the device for feeding hot molten metal. Thereafter, the injection cylinder 9 is returned to the position indicated by a solid line so as to be held uprightly and the block 18 is elevated by using the ram 19, thus fitting the injection sleeve 20 into a stationary sleeve 22 formed in the metal mold 7. Then, by actuating the injection cylinder 9 to elevate the plunger 16 within the injection sleeve 20, hot molten metal is injected into a cavity defined by the metal molds 7 and 8. After the hot molten metal is solidified and cooled subsequent to the completion of the injection, the moving platen 6 is raised by using the pull-back cylinder 5 to open the die, and thereafter the solidified product is taken out to the outside of the machine with the product take-out device. Finally, the cavity is cleaned and applied with a mold release by using the spraying device, thereby completing preparation for a next casting work. Thus, one casting cycle is completed.
However, the conventional die casting carried out with an apparatus constructed as above requires a good deal of time for completing one die casting cycle, resulting in poor productivity. FIG. 28A shows the times required for the respective steps of the die casting cycle when using the above-mentioned conventional die casting machine. As seen from this figure, it takes about 45 seconds for solidifying and cooling the product after injection, and about 40 seconds for cooling, cleaning and spraying the die after take-out of the product. Accordingly, about 114 seconds are required for completing one cycle. Thus, 70% or more of the total time in using a conventional apparatus is consumed by the steps preparatory to the die casting itself (i.e., die clamping, injection and die opening). This results in substantial waiting time and corresponding poor productivity.